1. Field of the Invention
The present invention relates to a variable valve-timing engine having a variable valve timing mechanism (a phase angle adjusting unit) for adjusting a relative phase angle of an exhaust cam for opening and closing an exhaust valve and an intake cam for opening and closing an intake valve.
2. Description of the Related Art
In general, as a phase angle adjusting unit for adjusting a relative phase angle (a valve timing) of an exhaust cam for opening and closing an exhaust valve and an intake cam for opening and closing an intake valve, there are proposed a unit for adjusting the phase angle of an intake cam relative to an exhaust cam, which is disclosed in JP-A-2000-320358, a unit for altering the phase angle of an exhaust valve relative to an intake valve, a unit for implementing a selective change-over between a high-speed cam and a low-speed cam based on the engine speed, and a combination of any of the unit with a unit for adjusting the phase angle of an intake cam relative to an exhaust cam to thereby alter the phase angle of an intake cam to an exhaust cam.
In controlling a phase angle adjusting unit of the type as described above, an oil pressure control unit is used in order to improve the response in control, and a correction to a control value for the phase angle adjusting unit is implemented in response to deterioration in viscosity of a hydraulic fluid.
When the user replaces oil, however, since a correction value learnt just before the replacement of oil continues to be used as it is as the control value for the phase angle adjusting unit, there is caused a problem that the control value becomes out of order which is adopted by the oil pressure control unit to control the operation of the phase angle adjusting unit.
Furthermore, since there is provided no unit for warning the user of deterioration in hydraulic fluid and suggesting the user to replace the hydraulic fluid so deteriorated with fresh hydraulic fluid, it sometimes happens that the user replaces wastefully hydraulic fluid which does not need to be replaced, or conversely, the user continues to use hydraulic fluid which needs to be replaced.
In particular, there is caused a problem that developing deterioration in oil reduces the response in controlling the phase angle adjusting unit.
The present invention was made in view of these situations, and a primary object thereof is to implement the initialization of a correction value for a control oil pressure value adopted by the oil pressure controlling unit for proper operation when oil is replaced, and a secondary object thereof is to detect a timing at which oil has to be replaced and to make the user attempt to replace deteriorated oil with fresh one.
With a view to attaining the primary object of the invention, according to a first aspect of the invention, there is provided a variable valve-timing engine having a phase angle adjusting unit for adjusting a relative phase angle of an exhaust cam for opening and closing an exhaust valve and an intake cam for opening and closing an intake valve, an oil pressure controlling unit for controlling the operation of the phase angle adjusting unit through the oil pressure of hydraulic fluid, a correcting unit for correcting a control oil pressure value adopted by the oil pressure controlling unit to control the operation of the phase angle adjusting unit based on the degree of deterioration of the hydraulic fluid, and an oil replacement detection unit for detecting the replacement of the hydraulic fluid, wherein the correcting unit initializes a correction value for a control oil pressure value adopted by the oil pressure controlling unit to control the operation of the phase angle controlling unit immediately an oil replacement has been implemented, so that a preset initial value can be used.
Namely, in the event that a correction value for a control oil pressure value adopted by the oil pressure controlling unit to control the operation of the phase angle adjusting unit continues to be used as it is as an initial value, the oil pressure control value becomes unsuitable for the operation of the phase angle adjusting unit, leading to improper adjustment of the phase angle. However, in the event that the initial value is used in a manner as has been described above, the phase angle adjusting unit can be operated properly.
With a view to attaining the secondary object of the invention, according to a second aspect of the invention, there is provided a variable valve-timing engine having a phase angle adjusting unit for adjusting a relative phase angle of an exhaust cam for opening and closing an exhaust valve and an intake cam for opening and closing an intake valve, an oil pressure controlling unit for controlling the operation of the phase angle adjusting unit through the oil pressure of hydraulic fluid, a correcting unit for correcting a control oil pressure value adopted by the oil pressure controlling unit to control the operation of said phase angle adjusting unit based on the degree of deterioration of the hydraulic fluid, an oil replacement detection unit for detecting the replacement of the hydraulic fluid and a deterioration indicating unit for indicating the replacement of the hydraulic fluid, wherein the correcting unit initializes a correction value for a control oil pressure value adopted by the oil pressure controlling unit to control the operation of the phase angle controlling unit immediately an oil replacement has been implemented, so that a preset initial value can be used.
According to the configuration, since the hydraulic fluid is replaced according to the indication by the deterioration indicating unit, this allowing for the oil to be replaced at a proper timing, not only can the wasteful replace of oil by the user be prevented but also the reduction in response in controlling the phase angle adjusting unit can be prevented.
In addition, since a correction value for the control oil pressure adopted by the oil controlling unit to control the operation of the phase angle adjusting unit is initialized immediately the oil replacement has been implemented, so that a preset initial value, the phase angle adjusting unit can be operated properly.
According to a third aspect of the invention, there is provided a variable valve-timing engine as set forth in the first or second aspect of the invention, wherein the initial value is a correction value adopted after the oil pressure controlling unit and the phase angle adjusting unit have been run in.
In the event that a correction value obtained after the required running-in has been completed properly is used as an initial value, the phase angle adjusting unit is allowed to operate properly, and the response and reliability in controlling can be improved as much as possible.